Vehicle

ABSTRACT

A vehicle includes an energy storage, a motor driver, an electric motor, and circuitry. The motor driver is configured to convert direct-current power to alternating-current power and to convert alternating-current power to direct-current power. The electric motor is connected to the energy storage via the motor driver to move the vehicle. The circuitry is configured to drive the electric motor with a first current value to consume excess electric power. The first current value is different from a minimum current value to generate regeneration power arising from a braking force. The circuitry is configured to drive the electric motor with a second current value smaller than the first current value if a temperature of the electric motor is higher than a first threshold temperature or a temperature of the motor driver is higher than a second threshold temperature.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 15/447,129 filed on Mar. 2, 2017, which claimspriority under 35 U.S.C. § 119 to Japanese Patent Application No.2016-041934, filed Mar. 4, 2016, entitled “Vehicle.” The contents ofthese applications are incorporated herein by reference in theirentirety.

BACKGROUND 1. Field

The present disclosure relates to a vehicle.

2. Description of the Related Art

A hybrid vehicle described in Japanese Unexamined Patent ApplicationPublication No. 2003-134602 includes an engine, a generation electricmotor driven by the engine, a drive electric motor, and a battery actingas an energy store for electric energy (see FIG. 1 of JapaneseUnexamined Patent Application Publication No. 2003-134602).

In the hybrid vehicle described in Japanese Unexamined PatentApplication Publication No. 2003-134602, in addition to braking controlto reduce the speed of a vehicle by controlling a braking device basedon the operation amount of a brake pedal and a deceleration requestcommand from a vehicle speed control unit, regenerative cooperativebraking is also performed to add, as braking force, regenerative torquefrom the drive electric motor.

In the hybrid vehicle described in Japanese Unexamined PatentApplication Publication No. 2003-134602, in a regeneration mode of thedrive electric motor, regenerative energy generated by the driveelectric motor in the regeneration mode is stored as electric energy inthe battery. Control is described therein for cases in which the desireddeceleration is not obtainable because the battery is unable to absorbthe regenerative energy of the drive electric motor due to the state ofcharge of the battery. In such cases, the generation electric motor iscontrolled so that the q-axis current is 0, the d-axis current<0, andregenerative energy from the drive electric motor unable to be absorbedby the battery is lost as heat in the generation electric motor, thedesired deceleration is obtained by absorbing the excess electric energy(see Japanese Unexamined Patent Application Publication No. 2003-134602paragraph [0019], FIG. 3A, and FIG. 3B).

SUMMARY

According to one aspect of the present invention, a vehicle includes anenergy storage, a motor driver, an electric motor, and circuitry. Themotor driver is configured to convert direct-current power toalternating-current power and to convert alternating-current power todirect-current power. The electric motor is connected to the energystorage via the motor driver to move the vehicle. The circuitry isconfigured to drive the electric motor with a first current value toconsume excess electric power. The first current value is different froma minimum current value to generate regeneration power arising from abraking force. The circuitry is configured to drive the electric motorwith a second current value smaller than the first current value if atemperature of the electric motor is higher than a first thresholdtemperature or a temperature of the motor driver is higher than a secondthreshold temperature.

According to another aspect of the present invention, a vehicle includesan energy storage, a motor driver, an electric motor, and circuitry. Themotor driver is configured to convert direct-current power toalternating-current power and to convert alternating-current power todirect-current power. The electric motor is connected to the energystorage via the motor driver to move the vehicle. The circuitry isconfigured to drive the electric motor with a first current value toconsume excess electric power. The first current value is different froma minimum current value to generate a driving force. The circuitry isconfigured to drive the electric motor with a second current valuesmaller than the first current value if a temperature of the electricmotor is higher than a first threshold temperature or a temperature ofthe motor driver is higher than a second threshold temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings.

FIG. 1 is a block diagram illustrating a schematic configuration of avehicle according to an embodiment.

FIG. 2 is a block diagram illustrating a schematic configuration of thevehicle in the example of FIG. 1, partially abbreviated to facilitateunderstanding of the vehicle.

FIG. 3 is a schematic electric circuit diagram illustrating an exampleconfiguration of the VCU portion, and the first and second inverterportion in FIG. 1 and FIG. 2.

FIG. 4 is an explanatory diagram of basic inefficient control of avehicle according to an embodiment.

FIG. 5 is an Id-Iq plane diagram to explain conventional efficientcontrol, and inefficient control.

FIG. 6 is a flowchart to accompany explanation of a specific operationof inefficient control of a vehicle according to the embodiment.

FIG. 7 is a characteristics chart illustrating battery receivable power.

FIG. 8 is a flowchart illustrating details of processing of step S7 inthe flowchart of FIG. 6.

FIG. 9 is an Id-Iq plane diagram to accompany explanation of expanding avoltage limit ellipse when a requested phase current and a post-step-upmaximum phase current are the same as each other.

FIG. 10 is an Id-Iq plane diagram to accompany explanation of expandinga voltage limit ellipse when a requested phase current is larger than apost-step-up maximum phase current.

FIG. 11 is a flowchart illustrating details of processing of step S17 inthe flowchart of FIG. 8.

FIG. 12 is a flowchart illustrating details of processing of step S18 inthe flowchart of FIG. 11.

FIG. 13 is an Id-Iq plane diagram to accompany explanation of overalloperation.

FIG. 14 is an explanatory diagram of operation of an embodiment.

FIG. 15 is a block diagram illustrating a schematic configuration of avehicle (electric car) of a modified example.

DESCRIPTION OF THE EMBODIMENTS

The embodiment(s) will now be described with reference to theaccompanying drawings, wherein like reference numerals designatecorresponding or identical elements throughout the various drawings.

Detailed explanation follows regarding preferable embodiments of avehicle according to the present disclosure, with reference to theaccompanying drawings.

Configuration

FIG. 1 is a block diagram illustrating a schematic configuration of avehicle (also called a car) 10 according to an embodiment.

The vehicle 10 basically includes an engine ENG, a drive system 11, ahigh voltage battery BATh, a low voltage battery BAT1, a voltage controlunit (VCU) 12, a first inverter INV1, a second inverter INV2, anelectronic servo brake (ESB), and a controller 14.

The drive system 11 includes a first motor-generator MG1 and a secondmotor-generator MG2, which are each a permanent magnet synchronous motor(a rotating electric motor, an electric motor) having a vectorcontrolled three-phase embedded magnet structure, an engine ENG, adriving force transmission state switching section 15, and a reductiongear D.

The driving force transmission state switching section 15 includes aclutch (not illustrated in the drawings) for coupling the engine ENG andthe reduction gear D together, and a transmission unit or fixed gearstage installed between the clutch and the reduction gear D.

In FIG. 1, the bold solid lines illustrate mechanical coupling, thedouble solid lines illustrate electrical wiring, and the fine solidlines illustrate control lines (including signal lines).

In the vehicle 10, the driving force transmission state switchingsection 15, and the mechanical couplings extending from the two sides ofthe driving force transmission state switching section 15, are onlyemployed when using the engine ENG as a drive source to drive wheels(drive wheels) W on the other side of the reduction gear D, through thedriving force transmission state switching section 15. Note thatconfiguration may be made such that both the engine ENG and the secondmotor-generator MG2 are employed during acceleration.

Note that the present disclosure is mainly applied in a state in whichthe driving force transmission state switching section 15 is employed todisengage the motive force of the engine ENG from the wheel (drivewheel) W side, and in which the second motor-generator MG2 drives thewheels (drive wheels) W.

Thus, as illustrated in FIG. 2, in order to avoid complication and forease of understanding, in the following, explanation of configurationand operation is based on block diagrams illustrating schematicconfigurations of the vehicle 10 not depicting the driving forcetransmission state switching section 15.

The engine ENG drives the first motor-generator MG1 as a generator. Insuch a situation, the first motor-generator MG1 generates electric powerby being driven by the rotational motive force of the engine ENG.

Moreover, in some cases the engine ENG functions as a mechanical load,with the crank shaft rotated in an idling state by being driven by thefirst motor-generator MG1 operating as an electric motor during brakingof the vehicle 10.

The second motor-generator MG2 for driving the vehicle 10 operates(acts) as an electric motor by being supplied with electric power fromat least one of the high voltage battery BATh or the firstmotor-generator MG1, and generates torque to move the vehicle 10. Thetorque generated by the second motor-generator MG2 is transmitted asdrive force through the reduction gear D to the wheels W. The secondmotor-generator MG2 also operates as a generator during braking of thevehicle 10.

The high voltage battery BATh includes plural storage cells connectedtogether in series, and, for example, supplies a high voltage of from100 V to 300 V. The storage cells are, for example, lithium ion cells ornickel hydride cells. The high voltage battery BATh may also beconfigured by a capacitor.

A converter CONV is a DC/DC converter that steps down a direct currentoutput voltage of the high voltage battery BATh to another directcurrent voltage. The low voltage battery BAT1 stores the voltage steppeddown by the converter CONV, and supplies a fixed voltage of, forexample, 12 V to an electrical component 18 such as a light contained inancillary equipment 16, and also acts as a direct current power sourcefor the controller 14, etc.

The VCU 12 steps up a voltage V1, which is the output voltage of thehigh voltage battery BATh, to a voltage V2, which is an input voltageused by the second motor-generator MG2 when the second motor-generatorMG2 operates as an electric motor.

The VCU 12 also steps down the voltage V2, which is the output voltageof the second motor-generator MG2 when the second motor-generator MG2 isoperating as a generator during braking of the vehicle 10, to thevoltage V1.

Moreover, when the second motor-generator MG2 is operating as agenerator during braking of the vehicle 10, the VCU 12 steps the voltageV2 up or down when driving the first motor-generator MG1 through thefirst inverter INV1 using this generated electric power.

Moreover, the VCU 12 steps down the voltage V2, generated by the firstmotor-generator MG1 due to the motive force of the engine ENG andconverted into a direct current voltage, to the voltage V1.

Namely, the VCU 12 functions as a step-up/step-down converter (a two-waytransformer) between the high voltage battery BATh and the firstmotor-generator MG1 or the second motor-generator MG2.

The electric power stepped down by the VCU 12 to the voltage V1 issupplied as electric drive power to an electric air compressor 20included in the ancillary equipment 16 and/or as charging power for thehigh voltage battery BATh.

FIG. 3 is a schematic electric circuit diagram illustrating connectionrelationships between the high voltage battery BATh, the VCU 12, thefirst inverter INV1, the second inverter INV2, the first motor-generatorMG1, and the second motor-generator MG2.

As illustrated in FIG. 3, the VCU 12 includes a smoothing capacitor, aninductor, and two, upper and lower arm, switching elements. VCU 12 stepsup the voltage V2 on the output side to a voltage higher than thevoltage V1 by taking the voltage V1 output by the high voltage batteryBATh as an input voltage and switching the upper and lower arm switchingelements ON or OFF. Moreover, the VCU 12 steps down the voltage V1 onthe output side to a voltage lower than the voltage V2 by taking thevoltage V2 output by the first inverter INV1 or the second inverter INV2as an input voltage and switching the two upper and lower arm switchingelements ON or OFF.

Note that the voltage V2 is equivalent to the voltage V1 in a state inwhich the two switching elements of the VCU 12 are not ON/OFF switched,and the upper side switching element is in an ON state, the lower sideswitching element is in an OFF state.

Moreover, as illustrated in FIG. 3, the first inverter INV1 transformsan alternating current voltage generated by the first motor-generatorMG1, driven by the engine ENG, into the direct current voltage V2.Moreover, sometimes the first inverter INV1 transforms the voltage V2,generated by the second motor-generator MG2 during braking of thevehicle 10 and transformed by the second inverter INV2, into alternatingcurrent voltage, and supplies three phase current to the firstmotor-generator MG1. The second inverter INV2 transforms the voltage V2into alternating current voltage, and supplies the three phase currentthereof to the second motor-generator MG2 (in power mode). Moreover, thesecond inverter INV2 transforms the alternating current voltagegenerated by the second motor-generator MG2 during braking of thevehicle 10, into the voltage V2 (in regeneration mode).

The electronic servo brake ESB illustrated in FIG. 1 and FIG. 2 brakesthe vehicle 10 using a hydraulic system controlled by a non-illustratedelectric motor according to a depression amount Bp, which is theoperation amount of a brake pedal 30 by a driver of the vehicle 10.

The controller 14, in addition to performing vector control of the firstinverter INV1, the first motor-generator MG1, the second inverter INV2,the second motor-generator MG2, and the VCU 12, also performs control ofthe engine ENG, the electronic servo brake ESB, and the ancillaryequipment 16.

Detailed explanation is given later of control by the controller 14, butin brief, the controller 14 acquires, as sensor outputs, the brakedepression amount Bp expressing the operation amount of the brake pedal30 from a depression amount sensor, and also acquires an acceleratoropening Ap expressing the operation amount of an accelerator pedal 32from an accelerator opening sensor, a vehicle speed Vs from a vehiclespeed sensor 34, and an acceleration a from an acceleration sensor 58.

The controller 14 also acquires, as sensor outputs, a residual capacitystate of charge (SOC) of the high voltage battery BATh from an SOCsensor 35, a temperature Ti1 of the first inverter INV1 from atemperature sensor 36 attached in the vicinity of the switching elementsthereof, a temperature Ti2 of the second inverter INV2 from atemperature sensor 37 attached in the vicinity of the switching elementsthereof, a temperature Tcoi1 of the first motor-generator MG1 from atemperature sensor 38 attached in the vicinity of the stator coilthereof, a temperature Tcoi2 of the second motor-generator MG2 from atemperature sensor 39 attached in the vicinity of the stator coilthereof, and a temperature Tatf of a cooling medium from a temperaturesensor 40 attached to a flow path of cooling oil (cooling medium)circulating inside the drive system 11. Note that the cooling oil coolsthe inside of the drive system 11, including the first and secondmotor-generators MG1, MG2.

Moreover, the controller 14 also acquires, as sensor outputs,revolutions/current/rotation angle position and the like from sensors(not illustrated in the drawings) of resolvers and the like of the firstand second motor-generators MG1, MG2. The controller 14 also acquires ashift position Ps (for example, a drive position D, a drive position B)expressing the position of a shift lever 42 from a shift positionsensor.

Explanation of Basic Inefficient Control

Explanation follows regarding basic operation of inefficient controlrelated to the first motor-generator MG1 of the vehicle 10 basicallyconfigured as described above (this being, as described later, mainlycontrol to apply a positive d-axis current Id to the motor-generator,also called strong field control), with reference to FIG. 4.

For example, when the accelerator pedal 32 is released when the vehicle10 is travelling downhill, the second motor-generator MG2 is switchedfrom a power mode state to a regeneration mode state. In such asituation, the second motor-generator MG2 operates as a generator, andimparts a braking force (regenerative braking) to the vehicle 10, andgenerates regenerative power. When there is no charging limit, thisregenerative power from the second motor-generator MG2 charges the highvoltage battery BATh through the second inverter INV2 and the VCU12, andbraking force acts on the vehicle 10 as regenerative braking.

However, when there is a charging limit, such as the high voltagebattery BATh being in a fully charged state, the receipt of regenerativepower by the high voltage battery BATH is limited.

Thus, in the present embodiment, when the receipt of regenerative powerfrom the second motor-generator MG2 by the high voltage battery BATh (bycharging) is limited, in other words when excess electric power isgenerated in the vehicle 10, the first motor-generator MG1 is driven asan electric motor with the voltage V2 through the first inverter INV1,and the engine ENG is idled as a load (called reverse-driving the engineENG). Namely, the regenerative power of the second motor-generator MG2is employed as energy to idle the engine ENG through the firstmotor-generator MG1.

FIG. 4 is an explanatory diagram illustrating a flow of energy duringbraking of the vehicle 10 when the first motor-generator MG1 is drivenas a generator by the regenerative power generated by the secondmotor-generator MG2, and the engine ENG is idled.

As illustrated in FIG. 4, when the first motor-generator MG1 is in powermode and driving the engine ENG in reverse, a step up in the voltage V2applied to the first motor-generator MG1 is obtained to the voltage V1by the VCU 12, and the first motor-generator MG1 is driven at aninefficient operation point by performing strong field control such thatthe d-axis current Id of the first motor-generator MG1 is increased tomainly a positive value (Id>0).

Note that in normal strong field control (the conventional inefficientcontrol/typical control in FIG. 5), the d-axis current Id notcontributing to torque generation is a negative value (Id<0), and vectorcontrol is performed to achieve the maximum generated torque for a givencurrent, as maximum torque/current (maximum torque per ampere (MTPA))control. However, in the present embodiment, the d-axis current Id isstepped up to a current value different from the minimum current of MTPAcontrol, and the first motor-generator MG1 is driven such that thed-axis current Id is mainly a positive value (more precisely, a currentvalue greater than the d-axis current IdO at the operation point P0 inFIG. 5, Id0<Id (and Id takes both negative and positive values)).

In such a case, the runnable range of the first motor-generator MG1 isincreased due to the voltage V2 applied to the first motor-generator MG1being stepped up. Moreover, the output efficiency is decreased in thefirst motor-generator MG1 subjected to strong field control, and thereis an increase in the amount of heat generated, mainly by copper loss inthe stator (armature) coil. The excess part of the regenerative power(excess electric power) of the second motor-generator MG2 is consumed bythe amount of heat generated.

Note that in the following explanation, stepping up of the voltage V2applied to the first motor-generator MG1 in power mode {for generatingtorque (drive torque/power torque in the rotation direction of the firstmotor-generator MG1)} or in regeneration mode {for generating torque inthe opposite direction to the rotation direction of the firstmotor-generator MG1 (braking torque/regenerative torque)}, and thestrong field control of the first motor-generator MG1, are referred tocollectively as inefficient control.

Next, explanation follows regarding operating points on dq-axiscoordinates (called the Id-Iq plane) in a motor-generator subject toinefficient control, as typified by the first motor-generator MG1, andregarding the voltage applied to the motor-generator, with reference tothe Id-Iq plane diagram of FIG. 5.

The range of the operating points of a motor-generator is limited by themaximum phase current Ia able to be supplied to the motor-generator, andby the voltage V2 applied to the motor-generator (the direct currentterminal voltage of the inverter).

The amplitude of the current (Id, Iq) of the motor-generator is limitedby the maximum phase current Ia, and so Equation (1) below (currentlimit circle) should be satisfied.Id ² +Iq ² ≤Ia ²  (1)

Wherein: Id is the d-axis current, Iq is the q-axis current, and Ia isthe maximum phase current. Note that Ia is also employed for a currentvector Ia, as Ia is a composite vector current of the current vector Idand the current vector Iq.

An induction voltage (Vd, Va) of the motor-generator is expressed byEquation (2) below. Note that normally Equation (2) is expressed inmatrix form.Vd=O×Id+(−ωLd)×Iq+OVq=(ωLd)×Id+O×Iq+ωψa  (2)

Wherein: ω is the angular velocity of the motor-generator, Lq is theq-axis inductance, Ld is the d-axis inductance, and ψa is the fluxlinkage (magnetic flux).

From Equation (2), the dq induction voltage (the magnitude of the vectorsum of the induction voltage Vd of the armature arising in the d-axisand the induction voltage Vq of the armature arising in the q-axis) Vois expressed by Equation (3) below.Vo=(Vd ² +Vq ²)^(1/2)=ω{(LdId+ψa)²+(LqIq)²}^(1/2)  (3)

The limit voltage of the voltage V2 illustrated in FIG. 2 is denotedVom. The limit voltage Vom is determined by the voltage V2, and therelationship therebetween is expressed by Equation (4) below, wherein kis a constant determined by the modulation system of switching controlof the VCU 12.Vom=kV2  (4)

As expressed by Equation (5) below, the dq induction voltage Vo needs tobe the limit voltage Vom or lower.Vo≤Vom  (5)

Namely, due to the range of operating points of the motor-generatorbeing limited by the voltage, Equation (6) below (voltage limit ellipse)from Equation (3) and Equation (5) needs to be satisfied.(LdId+ψa)²+(LqIq)²≤(Vom/ω)²  (6)

As stated above, the limit of operation of the motor-generator due tocurrent is expressed by Equation (1).

FIG. 5 illustrates the Id-Iq plane (dq coordinates). In this caseEquation (1) is represented by the region inside the current limitcircle (Ia²=Id²+Iq²) in dq coordinates, as illustrated in FIG. 5.

The limit to operation of the motor-generator due to voltage isexpressed by Equation (6). Equation (6) is represented by the regioninside the voltage limit ellipse {(LdId+ψa)²+(LqIq)²=(Vom/ω)²} in dqcoordinates, as illustrated in FIG. 5. The range of current able to besupplied to the motor-generator is the range satisfying both Equation(1) and Equation (6), and this range is illustrated by the hatched rangein FIG. 5.

The torque T of the motor-generator is expressed by Equation (7) below.T=Pn{ψaIq+(Ld−Lq)IdIq}  (7)

Wherein, Pn is the number of poles of the motor-generator. The firstelement on the right hand side is torque due to permanent magnets, andthe second element on the right hand side is reluctance torque.

An equation expressing an equivalent torque line (equivalent torquecurve, constant torque line, or constant torque curve) from solvingEquation (7) for Iq is expressed by Equation (8) below.Iq=T/(Pn{ψaIq+(Ld−Lq)Id})  (8)

Equation (8) is represented by a hyperbola with asymptotesId=ψa/(Lq−Ld), Iq=0 (the curves on the power side and regenerative sideof the equivalent torque lines T in FIG. 5).

In control of operating points of a motor-generator not subject toinefficient control, the following are, for example, performed: maximumtorque/current control to achieve maximum torque for a given current(control in which the current vector is orthogonal to the tangent to afixed torque curve at the operating points); or maximum efficiencycontrol to achieve the minimum loss taking into consideration not onlythe copper loss, but also core loss and the like (in which often theoperating points are further advanced in phase than in maximum torquecontrol, namely, the d-axis current Id is shifted toward the negativedirection).

In the example illustrated in FIG. 5, a motor-generator is being drivenat operating points (also referred to as intersection points) P0 etc.,on a curve of typical conventional efficiency control maximum torque perampere (MTPA) control.

In contrast thereto, in the inefficient control of the presentembodiment, as illustrated in FIG. 5, strong field control is performedsuch that the d-axis current Id of the motor-generator is, for example,a larger positive value, such as the value at operating point(intersection point) P4. The voltage V2 applied to the motor-generatorneeds to be raised in order to perform such strong field control. Theamplitude of the current Ia (Id, Iq) of the motor-generator is increaseddue to raising the voltage V2 applied to the motor-generator, enablingthe operating point of the motor-generator to be shifted. The torqueneeded for reverse-driving the engine ENG, this being a load on themotor-generator, is determined by friction, according to oil viscosity,etc., that changes with engine revolutions, temperature, and the like.However, qualitatively, since such torque asymptotically approaches afixed torque for smaller torque, the d-axis current Id is readilyshifted in the positive direction.

Moreover, when the limit voltage Vom of the voltage V2 is large and theangular velocity ω of the motor-generator is small, due to the area ofthe voltage limit ellipse of Equation (6) becoming larger, the amplitudeof the current Ia (Id, Iq) of the motor-generator is readily increased.

Thus, it is apparent that inefficient control of the motor-generator canbe efficiently performed by appropriately controlling the limit voltageVom of the voltage V2 and the angular velocity ω of the motor-generator.

Under inefficient control on the power side of the motor-generator(Id>Id0, Iq>0) in FIG. 5, the maximum phase current Imax prior tostepping up the voltage V2 is limited at the intersection point(operating point) P1 between the voltage limit ellipse and theequivalent torque line.

Note that under inefficient control on the regenerative side of themotor-generator (Id>Id0, Iq<0), the maximum phase current Imax prior tostepping up the voltage V2 is limited at the intersection point P1′between the voltage limit ellipse and the equivalent torque line.

Detailed Explanation of Operation of Inefficient Control

Detailed explanation follows regarding a specific example of inefficientcontrol (inefficient running) when a requested regenerative power Pregin the vehicle 10 is larger than the power receivable by the highvoltage battery BATh, with reference to the flowchart in FIG. 6.

At step S1, the controller 14 computes the requested regenerative powerPreg of the second motor-generator MG2. For the requested regenerativepower Preg, a target deceleration G is, as hitherto, computed based on aroad gradient (which may either be from a gradient detection sensor orfrom estimation), a shift position Ps of the shift lever 42 (such asdrive position D, drive position B), a degree of opening Ap of theaccelerator pedal 32 (in this case the degree of opening Ap=0 (state ofopening of the accelerator pedal 32)), vehicle speed Vs from the vehiclespeed sensor 34, and the depression amount Bp of the brake pedal 30. Therequested regenerative power Preg is then computed based on the targetdeceleration G.

The requested regenerative power Preg is computed here according to thedownslope gradient such that the vehicle speed Vs is substantiallyconstant.

Next, at step S2, the receivable power of the high voltage battery BATh(battery receivable power) Pbatin is computed.

As illustrated by the characteristics (map) in FIG. 7, the batteryreceivable power Pbatin=0 kW when the residual capacity SOC detected bya SOC sensor 35 is 100%.

When the residual capacity SOC is less than 100%, the battery receivablepower Pbatin is acquired by reference to the characteristics (map), withthe residual capacity SOC, and the battery temperature Tbat (forexample, from about −30° C. to about +50° C., as illustrated) as inputvalues. These characteristics are generated in advance, and arecharacteristics such that, for a given residual capacity SOC, the higherthe battery temperature Tbat, the larger the battery receivable powerPbatin. Similarly, for example, the characteristics are such that, for agiven battery temperature Tbat, the lower the residual capacity SOC, thelarger the battery receivable power Pbatin.

Next, at step S3, an auxiliary power consumption Paux is computed. Theauxiliary power consumption Paux is computed by summing the electricpower consumption of the electrical air compressor 20, the electricpower consumption of the converter CONV, and the electric powerconsumption of the electrical component 18.

Next, at step S4, determination is made as to whether or not there is aneed to implement inefficient running. In such cases, if the requestedregenerative power Preg is consumable by the battery receivable powerPbatin and the auxiliary power consumption Paux (Preg≤Pbatin+Paux), thenthe requested regenerative power Preg can be consumed (including bycharging) in the vehicle 10 without performing inefficient running. Aninefficient running flag Fi is accordingly reset (Fi←0). However, if therequested regenerative power Preg is greater than the combined electricpower consumption of the battery receivable power Pbatin and theauxiliary power consumption Paux (Preg>Pbatin+Paux), determination ismade that inefficient running needs to be performed, and the inefficientrunning flag Fi is set (Fi←1).

Next, at step S5, determination is made as to whether the inefficientrunning flag Fi is set (Fi=1) or not (Fi=0).

When the inefficient running flag Fi is not set (Fi=0) (NO at step S5),there is no need to consume the requested regenerative power Preg of thesecond motor-generator MG2 in the inefficient region of the firstmotor-generator MG1 (herein, also referred to simply as the electricmotor). Therefore, at step S6, an electric motor inefficient regionpower consumption Pine is set to zero (Pine←0), and processing returnsto step S1.

When the inefficient running flag Fi is set (Fi=1) (YES at step S5), theelectric motor inefficient region power consumption Pine is computed atstep S7, and an electronic-servo-brake power allocation Pesv iscomputed.

FIG. 8 is a detailed flowchart of step S7.

At step S7 a, a required phase current value computed from the requestedregenerative power Preg is taken as a requested phase current Ireq.

As illustrated in FIG. 5, the requested phase current Ireq is largerthan the prior-to-step-up maximum phase current Imax (=Ia), and so, atstep S7 b, in order to secure the requested phase current Ireq, thelimit voltage Vom for the voltage V2 is stepped up by the VCU 12 to alimit voltage V′om, and the voltage limit ellipse is expanded asexpressed in the following Equation (6′).(LdId+ψa)²+(LqIq)²≤(V′om/ω)²  (6′)

Next, at step S7 c, a limit power consumption in the electric motorinefficient region after step up is set as the electric motorinefficient region power consumption Pine.

Next, at step S7 d, the magnitudes (absolute values) of the requestedphase current Ireq and a post-step-up current (also referred to as thecurrent limit circle phase current) I′max of the current limit circleare compared, and determination is made as to whether or not|Ireq|>|I′max|.

When the magnitude of the requested phase current Ireq is smaller than,or equal to, the magnitude of the current limit circle phase currentI′max (NO at step S7 d), there is no need for a power allocation to theelectronic servo brake ESB. Hence, at step S7 e, theelectronic-servo-brake power allocation 1 is set to 0.

In such a situation, as illustrated in FIG. 9, the voltage limit ellipseexpressed by Equation (6) is expanded to the post-VCU step-up voltagelimit ellipse expressed by Equation (6′) by the VCU 12 stepping up(stepping up voltage V2 such that limit voltage Vom becomes limitvoltage V′om) so as to enable the relationship requested phase currentIreq=I′max to be secured.

When doing so, in order to enable consumption of the requestedregenerative power Preg as heat by inefficient control of the firstmotor-generator MG1, the intersection point P1 of the pre-step-upmaximum phase current Imax is changed to further along an equivalenttorque line in the strong field direction (a direction to furtherincrease the positive value of the d-axis current), as far as theintersection point P2 (=P4) of the post-step-up maximum phase currentI′max.

However, there is a need for an allocation of power to the electronicservo brake ESB when determined at step S7 d that the magnitude of therequested phase current Ireq is larger than the magnitude of the currentlimit circle phase current I′max (YES at step S7 d). Hence, at step S7f, the electronic-servo-brake power allocation 1 is set to Ra(Ireq²−I′max²).

In such cases, as illustrated in FIG. 10, the post-VCU step-up voltagelimit ellipse expressed by Equation (6′) is expanded to a rangeintersecting with the current limit circle, which is the limit ofcapability of the VCU 12. When doing so, in order to enable consumptionof the requested regenerative power Preg as heat by inefficient controlof the first motor-generator MG1, the intersection point P1 of thepre-step-up maximum phase current Imax is changed to further along anequivalent torque line in the strong field direction (a direction tofurther increase the positive value of the d-axis current), as far asthe intersection point P2 (=P4) of the post-step-up maximum phasecurrent I′max. The amount of the requested electric power portion Ra(Ireq²−I′max²) from the intersection point P2 to the point P4 isconsumed by the electronic servo brake ESB as the electronic-servo-brakepower allocation 1. As a result, the braking force due to the electronicservo brake ESB is added to the regenerative braking force of the secondmotor-generator MG2.

Next, at step S17, during performing, or as a result of performing,electric motor inefficient running with an expanded voltage limitellipse, determination processing is performed as to whether or not alimit temperature of the first motor-generator MG1 has been reached, asa heat damage condition.

FIG. 11 is a detailed flowchart of step S17.

At step S17 a, an electric motor coil temperature Tcoil is acquired bythe temperature sensor 38 (FIG. 2), for example a thermistor provided tothe electric motor coil of the first motor-generator MG1.

Moreover, at step S17 b, a cooling medium temperature Tatf, which is thetemperature of oil for cooling the first motor-generator MG1, isacquired from the temperature sensor 40.

Next, at step S17 c, determination is made as to whether or not theelectric motor coil temperature Tcoil is less than a thresholdtemperature value Th1, which is a control temperature (Tcoi1<Tth1), andthe cooling medium temperature Tatf is less than a threshold temperaturevalue Th2, which is a control temperature (Tatf<Th2).

When the determination of step S17 c is affirmative (Tcoil<Th1, andTatf<Th2) (YES at step S17 c), determination is made that the firstmotor-generator MG1 is not subject to heat damage, and, at step S17 d, aheat damage flag Fheat is reset (Fheat←0), and processing returns tostep S1.

However, determination at step S17 c is negative (NO at step S17 c) whenat least one of the temperature determinations is negative duringtemperature determination at step S17 c. In such cases, since the firstmotor-generator MG1 needs to be protected from heat damage, first theheat damage flag Fheat is set (Fheat←1) at step S17 e.

Next, at step S17 f, the conditions of the heat damage condition Vomrelated to the voltage limit ellipse are changed, and, at step S18, thetotal power allocation of the electronic servo brake ESB is computed.

Explanation follows regarding processing of step S17 f and step S18,with reference to FIG. 13.

When the heat damage condition Fheat=1 is established, the V′om isreturned to V^(heat)om as illustrated by Equation (5″) below, namely,the voltage V2 is lowered, and the electric motor inefficient region iscontracted to a voltage limit ellipse enabling running even at hightemperature. In such cases, the phase current Imax is decreased tointersection point P5 while tracing along an equivalent torque line ofelectric motor shaft end requested torque characteristics.(LdId+ψa)²+(LqIq)²≤(V ^(heat) om/ψ)²  (5″)

In such cases, a total power allocation Pesball of the electronic servobrake ESB is computed at step S18.

FIG. 12 is detailed flowchart of step S18.

At step S18 a, the determination content explained in step S17 c isemployed again to determine whether or not the heat damage flag Fheat isFheat=1, or Fheat=0. When the heat damage flag Fheat is Fheat=0, sincethe heat damage condition has been cleared, the phase current Ia of thephase current I^(heat)max is returned along the equivalent torque lineto phase current I′max, switching from the operating point (intersectionpoint) P5 to the operating point (intersection point) P3. Thereby, asillustrated in step S18 b, the total power allocation Pesball of theelectronic servo brake ESB (also referred to as theelectronic-servo-brake power allocation ALL) can be returned to thepower allocation 1 of the electronic servo brake ESB computed at step S7f.

However, when determined at step S18 a that the heat damage flag Fheatis Fheat=1, since the heat damage condition has not been cleared, at theoperating point (intersection point) P5 of the phase currentI^(heat)max, the total power allocation Pesball of the electronic servobrake ESB is the combined power of the electronic-servo-brake powerallocation 1 for the portion from the operating point (intersectionpoint) P3 to the operating point (intersection point) P4=Ra(Ireq²−I′max²), as computed at step S7 f, and the electronic-servo-brakepower allocation 1 from operating point (intersection point) P3 tooperating point (intersection point) P5=Ra (I′max²−I^(heat)max²). Thetotal power allocation Pesball is allocated for consumption in theelectronic servo brake ESB.

The first motor-generator MG1 can thereby be protected from heat damage.

Note that by, at step S17 described above, contracting the voltage limitellipse when the heat damage condition is established, the running pointof the electric motor is moved from P3 to P5. However, the running pointof the electric motor may be shifted from P3 to P5 without contractingthe voltage limit ellipse, namely, without lowering the voltage V2(stepped-up voltage).

SUMMARY AND MODIFIED EXAMPLES OF EMBODIMENTS

The vehicle 10 according to the present embodiment includes: the highvoltage battery BATh, serving as an energy storage device; the first andsecond inverters INV1, INV2 serving as a drive device (a motor driver)capable of two-way conversion between direct current and alternatingcurrent; the first motor-generator MG1 and/or the second motor-generatorMG2 serving as rotating electric motor(s) connected to an alternatingcurrent side of the first and second inverters INV1, INV2 serving as thedrive device, and having an output shaft connected to a load (the engineENG serving as a load of the first inverter INV1 and/or the wheels Wserving as the load of the second inverter INV2); the VCU 12 serving asa voltage transformer having a low voltage side (voltage V1 side)connected to the high voltage battery BATh and a high voltage (voltageV2) side connected to a direct current side of the first and secondinverters INV1, INV2, the voltage transformer stepping up the voltage V1of the high voltage battery BATh to the voltage V2, and applying thestepped-up voltage V2 to the first and second motor-generators MG1, MG2through the first and second inverters INV1, INV2, respectively; and thecontroller 14 that controls the first and second inverters INV1, INV2,the first and second motor-generators MG1, MG2, and the VCU 12.

FIG. 13 mentioned above is a diagram of the Id-Iq plane to accompanyexplanation of the overall operation.

When excess electric power is generated in the vehicle 10, for example,in cases in which part or all of the regenerative power Preg of thesecond motor-generator Mg2 is excess, and although consumption isperformed in the ancillary equipment 16, the residual capacity SOC is100% and charging of the high voltage battery BATh is not possible, thecontroller 14 expands the running range of the first motor-generator MG1by stepping up the voltage V2, this being the voltage stepped-up by theVCU 12 (limit voltage Vom) (to, for example, the limit voltage V′om atintersection point P3 in FIG. 13). A current value accordingly arisesdifferent to the minimum current value for the first motor-generator MG1to generate a specific drive force (the current value at operating pointP0 under the conventional efficient control of FIG. 13) (a current valuelarger than the d-axis current value (called the d-axis thresholdcurrent value) Id0 at the operating point P0 in FIG. 13 (Id>Ido)).

Then, driving the first motor-generator MG1 in the expanded runningrange, enables the excess electric power, for example part or all of theregenerative power Preg of the second motor-generator MG2, to beconsumed by the first motor-generator MG1.

During consumption, if the temperature of the first motor-generator MG1exceeds a predetermined threshold temperature value Tth, respectivelycorresponding to a coil temperature Tcoi1 raised by copper loss, or atemperature Ti1 of the first inverter INV1 or a temperature Tatf of acooling medium, then the stepped-up voltage V2 is decreased, the runningrange of the first motor-generator MG1 is contracted, and the electricpower consumption of the first motor-generator MG1 is decreased (forexample, to a limit voltage V^(heat)om, at operating point (intersectionpoint) P5 in FIG. 13).

Due to performing such control, excess electric power generated in thevehicle 10, which is neither able to be consumed in the ancillaryequipment 16 nor charged in the high voltage battery BATh, can beconsumed, and overheating of the first motor-generator MG1 or the firstinverter INV1 can be prevented.

Note that the d-axis current Id is increased along the equivalent torqueline when expanding the running range of the first motor-generator MG1by stepping up the voltage V2, and the d-axis current Id is decreasedalong the equivalent torque line when decreasing the stepped-up voltageV2. This enables the electric power consumption by the firstmotor-generator MG1 to be varied, while holding the shaft end torque(the torque arising at the output shaft) of the first motor-generatorMG1 constant.

In particular, when the d-axis current Id is strong field controlled(inefficiently controlled) so as to be a positive value, a secondaryadvantageous effect is achieved of being able to prevent a reduction inmagnetism of permanent magnets accompanying a rise in temperature of thefirst motor-generator MG1. Namely, due to the strong field control(inefficient control), even though permanent magnets reach a hightemperature, due to a magnetic field being applied to the permanentmagnets in the direction of magnetization and a demagnetizing field notbeing applied to the permanent magnets, the resistance todemagnetization is raised.

In addition, due to the strong field control (inefficient control), aneffect is exhibited of raised attraction force (magnetic restraintforce) between the non-illustrated permanent magnets of the rotor andarmature of the stator, the magnetic restraint force in the rotationdirection of the rotor and the axial direction of the rotor is raised,and a secondary effect is exhibited of improving the NV characteristicsof the first motor-generator MG1.

In this case, when the excess electric power generated by the vehicle 10itself is the regenerative power Preg arising from braking use, brakingforce due to the regenerative power Preg is provided by electric powerconsumption through power running the first motor-generator MG1, and anyinsufficiency still arising is supplemented by mechanical brakes, inthis embodiment by the electronic servo brake ESB, thereby securingbraking force. Moreover, the behavior of the vehicle is suppressed fromchanging due to control being performed along the equivalent torqueline.

The vehicle 10 is a hybrid vehicle, and the present embodiment enablesthe intervention of mechanical braking to be suppressed to a minimum,enabling prolonged usage of friction members for mechanical braking. Thefriction members for mechanical braking can also be reduced in size ifthe same usage duration as normal is to be achieved.

Simple explanation follows regarding the operation of the presentembodiment, with reference to FIG. 14.

When charging of the high voltage battery BATh is possible, the brakingforce on wheels W is secured by the regenerative power of the secondmotor-generator MG2 and the heat generation of the electronic servobrake ESB (the electronic-servo-brake power allocation 1), and theregenerative power charges the high voltage battery BATh. The generatedpower of the first motor-generator MG1 rotated by the engine E alsocharges the high voltage battery BATh (the top section in FIG. 14).

When charging of the high voltage battery BATh is limited (the highvoltage battery BATh is fully charged), and when there is no heat damageto the first motor-generator MG1, etc., the engine ENG is idled by powerrunning the first motor-generator MG1 along the equivalent torque lineof the inefficient region using the regenerative power Preg of thesecond motor generator MG2. The regenerative power Preg is convertedinto heat in the inefficient region of the first motor-generator MG1(the intersection point P2=P3 in FIG. 13). In such cases, the heatgenerated by the electronic servo brake ESB is not changed (the middlesection in FIG. 14).

However, when charging the high voltage battery BATh is limited (thehigh voltage battery BATh is fully charged), and there is heat damage tothe first motor-generator MG1, etc., as explained in the embodimentabove, the engine ENG is idled by power running the firstmotor-generator MG1 using the regenerative power Preg of the secondmotor generator MG2 along the equivalent torque line of the inefficientregion of the first motor-generator MG1, and the regenerative power Pregis converted into heat in the inefficient region of the firstmotor-generator MG1; however, the electric power consumption in theinefficient region is reduced as indicated by the hatched region(intersection point P5 in FIG. 13). The electronic servo brake ESBallocation portion is increased by this amount, and so the heatgenerated by the electronic servo brake ESB is increased (the bottomsection in FIG. 14).

Thus in the embodiment described above, when determined that thetemperatures of the elements (components) configuring the secondmotor-generator MG2 and the second inverter INV2 are a controltemperature or above, the VCU 12 stepped-up voltage V2 is lowered, so asto lower the upper limit to the running range of the inefficient regionof the second motor-generator MG2.

Such a configuration enables damage to the second motor-generator MG2and the second inverter INV2 due excessive rise in temperature to beforestalled, by merely changing control (without increasing cost),without adding a new device (without changing the configuration).Moreover, the behavior of the vehicle 10 can also be suppressed frombeing affected.

MODIFIED EXAMPLES

FIG. 15 is a block diagram illustrating a schematic configuration of avehicle 10A of a modified example.

The vehicle 10A of the modified example is what is referred to as anelectric car. In the vehicle 10A during, for example, travel on a longdownward slope (during a descent), when regenerative power Preg of thesecond motor-generator MG2 is generated in excess, the excess electricpower can be consumed by operating the second motor-generator MG2 in theinefficient region (Id>Id0, particularly Id>0) along the equivalenttorque line (regeneration) on the regeneration side (Id>0, Iq<0)illustrated in FIG. 5, similarly to as explained in the previousembodiment.

Note that the voltage V2 may be stepped up on the regeneration side, andinefficient control performed during regeneration by the secondmotor-generator MG2 in the expanded running range.

Note that the present disclosure is not limited to the aboveembodiments, and obviously various configurations may be adopted basedon the content of the present specification.

The present disclosure describes a vehicle capable of consuming excesselectric power generated in the vehicle by using a rotating electricmotor, without causing a deterioration of NV characteristics. Moreover,while suppressing vehicle behavior from being affected, the vehicle isalso capable of preventing excessive heating of the rotating electricmotor or a drive device if, during consumption of the excess electricpower, the temperature of the rotating electric motor or the temperatureof the drive device exceeds a threshold temperature value.

The present disclosure describes a vehicle including a rotating electricmotor, the vehicle including an energy storage device, a drive devicecapable of two-way conversion between direct current and alternatingcurrent, and a rotating electric motor connected to an alternatingcurrent side of the drive device and having an output shaft connected toa load. The vehicle also includes a voltage transformer having a lowvoltage side connected to the energy storage device and a high voltageside connected to a direct current side of the drive device. The voltagetransformer steps up the voltage of the energy storage device, andapplies the stepped-up voltage to the rotating electric motor throughthe drive device. The vehicle also includes a controller that controlsthe drive device, the rotating electric motor, and the voltagetransformer. The controller drives the rotating electric motor with afirst current value, different from a minimum current value for therotating electric motor to generate a specific drive force, so as tocause excess electric power to be consumed by the rotating electricmotor. The controller also, when a temperature of the rotating electricmotor or a temperature of the drive device exceeds a thresholdtemperature value, drives the rotating electric motor with a secondcurrent value smaller than the first current value and decreases theelectric power consumption of the rotating electric motor.

According to this aspect of the present disclosure, when an excess ofelectric power (excess electric power) is generated in the vehicle, theexcess electric power generated in the vehicle is consumable by therotating electric motor, under conditions in which the temperature ofthe rotating electric motor and the temperature of the drive device arenot high, and are a threshold value or lower, by expanding a runningrange of the rotating electric motor in an inefficient region (a regionof current values different to the minimum current value for therotating electric motor to generate a specific drive force). Moreover,overheating of the rotating electric motor or the drive device can beprevented by reducing the electric power consumption of the rotatingelectric motor if, during consumption of the excess electric power bythe rotating electric motor, the temperature of the rotating electricmotor or the temperature of the drive device exceeds their respectivethreshold temperature value.

In such cases, when changing a phase current supplied to the rotatingelectric motor from the first current value to the second current value,the controller may decrease the phase current along an equivalent torqueline. Decreasing the phase current along an equivalent torque lineenables electric power consumption by the rotating electric motor to bevaried, while holding the shaft end torque of the rotating electricmotor (the torque arising at the output shaft) constant.

Moreover, the controller may expand a running range of the rotatingelectric motor by stepping up the voltage of the energy storage deviceusing the voltage transformer, and drive the rotating electric motor inthe expanded running range such that current supplied to the rotatingelectric motor is the first current value. When the temperature of therotating electric motor or the temperature of the drive device exceedsthe threshold temperature value, the controller may lower the stepped-upvoltage and contract the running range, and drive the rotating electricmotor in the contracted running range such that the current supplied tothe rotating electric motor is the first current value.

Due to being able to control expansion or contraction of the runningrange by controlling the stepped-up voltage, the phase current suppliedto the rotating electric motor can be made smaller by lowering thestepped-up voltage when the temperature of the rotating electric motoror the temperature of the drive device has exceeded the thresholdtemperature value (namely, the operating point can be shifted such thatthe current is smaller). This accordingly enables control when shiftingthe operating point to be suppressed from becoming complicated.

When excess electric power generated by the vehicle is regenerationpower arising from braking use, and the regeneration power is not allconsumable in the rotating electric motor, preferably the controllersets braking force for the non-consumable portion of regeneration powerto be provided by mechanical braking. Thereby, when excess electricpower generated by the vehicle itself is regeneration power arising frombraking use, braking force due to the regenerative power is provided byelectric power consumption through power running the rotating electricmotor, and any insufficiency still arising is supplemented by mechanicalbrakes, thereby securing braking force. Moreover, the rotating electricmotor is controlled along an equivalent torque line, and so the behaviorof the vehicle can be suppressed from being affected.

Moreover, the temperature of the rotating electric motor may be atemperature of a field coil configuring the rotating electric motor or atemperature of a cooling medium for cooling the rotating electric motor,and the temperature of the drive device may be a temperature of asemiconductor switching element configuring the drive device. Thereby,the temperature of the rotating electric motor or the temperature of thedrive device can be simply and accurately reflected.

More specifically, the running range of the rotating electric motor maybe expanded by operating under strong field control. The d-axis currentis a positive value due to being strong field controlled (inefficientcontrolled), thereby enabling demagnetization of permanent magnetsaccompanying a rise in temperature of the rotating electric motor to beprevented. Even when the magnets have reached a high temperature, due tothe strong field control (inefficient control), a demagnetizing field isnot applied to the magnets and a magnetic field is applied in thedirection of magnetization, raising the resistance to demagnetization.Moreover, in strong field control, the attraction force due to themagnetism between the magnets of the rotor and the coil of the armatureis raised, enabling movement in both the rotation direction of the rotorand the axial direction of the rotor to be suppressed, and improving theNV characteristics of the rotating electric motor, and hence raising theNV characteristics of the vehicle.

The present disclosure is preferably applied to a vehicle in which thedrive device is a first drive device, the load is an internal combustionengine, the rotating electric motor is a first rotating electric motor,and the vehicle further includes the following: a second rotatingelectric motor having a wheel as a load, and a second drive devicehaving an alternating current side connected to the second rotatingelectric motor and a direct current side connected to the high voltageside of the voltage transformer. In such a configuration, excesselectric power generated by the vehicle is part or all of regenerationpower generated by the second rotating electric motor.

Namely, the present disclosure is preferably applied to a hybridvehicle. The present disclosure enables intervention of mechanicalbraking to be suppressed to a minimum, so as to enable prolonged usageof friction members for mechanical braking. The friction members formechanical braking can also be reduced in size if the same usageduration as normal is to be achieved.

Moreover, when the temperature of the rotating electric motor or thetemperature of the drive device has exceeded the threshold temperaturevalue during consumption of the excess electric power in the rotatingelectric motor, the stepped-up voltage is made smaller in theinefficient region, the running range of the rotating electric motor iscontracted, and overheating of the rotating electric motor or the drivedevice can be prevented by reducing the electric power consumption ofthe rotating electric motor.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A vehicle comprising: an energy storage; a motor driver configured to convert direct-current power to alternating-current power and to convert alternating-current power to direct-current power; an electric motor connected to the energy storage via the motor driver to move the vehicle; and circuitry configured to drive the electric motor with a first current value to consume excess electric power, the first current value being different from a minimum current value to generate regeneration power arising from a braking force, and drive the electric motor with a second current value smaller than the first current value if a temperature of the electric motor is higher than a first threshold temperature or a temperature of the motor driver is higher than a second threshold temperature.
 2. The vehicle according to claim 1, wherein when changing a phase current supplied to the electric motor from the first current value to the second current value, the circuitry decreases the phase current along an equivalent torque line.
 3. The vehicle according to claim 1, wherein the circuitry is configured to execute strong field control to drive the electric motor with the first current value or the second current value with respect to the minimum current value.
 4. The vehicle according to claim 1, wherein the temperature of the electric motor is a temperature of a field coil configuring the electric motor or a temperature of a cooling medium for cooling the electric motor, and the temperature of the motor driver is a temperature of a semiconductor switching element configuring the motor driver.
 5. A vehicle comprising: an energy storage; a motor driver configured to convert direct-current power to alternating-current power and to convert alternating-current power to direct-current power; an electric motor connected to the energy storage via the motor driver to move the vehicle; and circuitry configured to drive the electric motor with a first current value to consume excess electric power, the first current value being different from a minimum current value to generate a driving force, and drive the electric motor with a second current value smaller than the first current value if a temperature of the electric motor is higher than a first threshold temperature or a temperature of the motor driver is higher than a second threshold temperature.
 6. The vehicle according to claim 5, wherein when changing a phase current supplied to the electric motor from the first current value to the second current value, the circuitry decreases the phase current along an equivalent torque line.
 7. The vehicle according to claim 5, wherein the circuitry is configured to execute strong field control to drive the electric motor with the first current value or the second current value with respect to the minimum current value.
 8. The vehicle according to claim 5, wherein the temperature of the electric motor is a temperature of a field coil configuring the electric motor or a temperature of a cooling medium for cooling the electric motor, and the temperature of the motor driver is a temperature of a semiconductor switching element configuring the motor driver. 